Cruising the Solar System Postcards from the Planets Philip Stooke
NASA and other space agencies have been exploring the solar system for 50 years What have we learned from recent missions? Moons of Jupiter
Planets used to belong to astronomers but now they are studied mostly by geologists. Some planets are very active (volcanoes and quakes, or erosion by wind and water) Others never changed since they formed (so just craters) Some started out active but soon stopped (they took early retirement)
Looking back at Earth - as we begin our cosmic cruise
Earth: continents and oceans Water is apparent everywhere clouds, rivers, lakes and oceans Zoom in and life becomes visible from plants to highways
Earth: volcanoes and craters Violent events have shaped our world Volcanic eruptions, asteroid impacts, continents moving and pushing up mountains Kamchatka Manicouagan, Quebec
Earth: rivers and glaciers Water, always on the move, erodes the land so very few really ancient rocks remain. We live on a dynamic planet but what are the neighbors like?
The Moon first port of call A very different world. Millions of craters, not the few seen on Earth. Volcanoes and lava flows long ago, but now cold and inactive. The Moon is like a geological museum. One lesson: Earth had similar craters in the past.
The Moon old volcanoes and lava flows Hortensius domes (topography) Cinder cones Prinz lava channels
Lunar Reconnaissance Orbiter images Apollo 12 Luna 21 Lunokhod 2 Hyginus volcanic vents Fractured boulder
Water on the Moon 1999 Lunar Prospector The Moon has no water or so we used to say. Now we see that ice is found in shadows in craters at the poles 2009 - LCROSS 2009 Chandrayaan 1 - MMM
So Earth and the Moon are very different. How do other worlds compare? NASA
Mercury craters and lava flows In 1974 Mariner 10 suggested Mercury was much like the Moon. Now we have better pictures from the MESSENGER spacecraft. Mercury may have been more active than the Moon, but now it s also dead.
Mercury volcanic ash eruptions and lava plains They may be more extensive than on the Moon MESSENGER false color images: Orange = volcanoes Lava flows
Mercury global compression: did the planet shrink? Mercury is bigger than the Moon and may have been more active.
Venus volcanoes, mountains and fractures. A very active planet under its cloudy atmosphere. Volcanoes are probably still erupting. NASA s Magellan spacecraft made these radar images of lava flows and volcanoes
Venus craters and channels Very few craters all the old ones were covered by the lava. Channels up to thousands of miles long, cut by lava (too hot for water)
Venus from the surface - a stifling desert Venus is slightly smaller than Earth, almost as active, but less eroded because it s too hot for liquid water. Soviet Venera images
Mars intermediate in size and activity ESA Rosetta image
Mars plenty of craters, but more eroded than on the Moon
Mars giant volcanoes, lava flows, possibly some activity even now
Mars dry river beds? Mars was wet in the past. Now it s too cold for water but still has plenty of ice. Eberswalde fossil delta Warrego Valles dry stream beds
Moons of Mars - too small to be active, or even round Most worlds less than 500 km across don t have enough gravity to make themselves spherical Phobos 25 km across Deimos 15 km across Mars Reconnaissance Orbiter images
The inner planets tell a nice simple story: Small worlds are less active, large worlds are more active Early retirement Still going strong Moon Mercury Mars Venus Earth
Giant planets great balls of gas They all have solid rocky cores like Earth itself. They all have rings, but only Saturn s are easy to see. They all have lots of moons Jupiter Saturn Uranus Neptune
Moons of Jupiter Scientists once feared they would be boring Io Europa Ganymede Callisto Closest to Jupiter Most distant
Io covered with active volcanoes Io is heated by Jupiter s gravity by strong tides in its rocky body Galileo image New Horizons images
Europa Ice floating on a global ocean? Very few craters. A young, active surface on a world smaller than our Moon
Ganymede the biggest moon of all, bigger than Mercury. A fractured surface and a magnetic field maybe an ocean deep inside. Not as active as Europa, but it s been busy. Galileo images
Callisto wall-to-wall craters, huge concentric ring structures, bizarre ice spires - is the sun evaporating a surface of dirty ice? No fractures, no internal heat, another retired moon.
What pattern of activity? Close to Jupiter, very active - far from Jupiter, not active (Jupiter is the source of the energy) Io Europa Ganymede Callisto Closest to Jupiter Most distant
Saturn bright rings and many moons. What pattern will we find among the moons of Saturn? NASA Hubble Space Telescope
Small moons take the rough with the smooth Atlas Telesto Phoebe Hyperion Are some moons covered with dust from the rings?
Mimas not much happens here except impacts -but why does the largest crater have a bathtub ring?
Enceladus - next door to Mimas and only 500 km across, but always active: jets of water vapor erupt from cracks at its south pole. The surface has a few craters, but most areas are smooth or cracked. A very active little world.
Enceladus a deeply fractured surface. Jets emerge from warm cracks is there a liquid ocean underneath?
Tethys giant crater, giant valley. All its fractures are concentrated in one place, like the East African Rift Valley
Dione bright and dark and cracked all over. Scientists wonder if water is erupting from Dione as well, none seen yet.
Rhea another moon that took early retirement. We ve been moving out from Saturn no pattern of activity yet. But no two moons are the same.
Iapetus taking it to extremes. The greatest contrast from one side to the other in the solar system. Weak sunlight evaporates ice out of the warmer dark soil. It condenses back onto the colder bright areas.
Iapetus where did you get that ridge? A mountain ridge 20 km high in places runs around 75% of the equator Icy blotches on one of the mountains
Titan as big as Mercury, and the only moon with a thick atmosphere.
Titan radar looks through the clouds. And what a world it sees! methane lakes, riverbeds, sand dunes, volcanoes an active world. Lakes at the poles Craters but not many Sand dunes around the equator
Titan another way to see the surface go there! The European Space Agency s probe Huygens landed on Titan in 2005. It saw dry riverbeds that flow with liquid methane after rainstorms. ESA
Saturn s moons - no obvious pattern at all The Cassini spacecraft is still exploring Saturn NASA Hubble Space Telescope
Saturn s Rings put on a show Shadows show lumps in the otherwise very flat rings. One moon stirs up a narrow ringlet every time it comes close.
Uranus and Neptune Gas giants, but very different from Jupiter and Saturn. Lots of methane, not much hydrogen. Neptune from Voyager 2 Uranus from Hubble Space Telescope Both sets of rings have been artificially brightened
Moons of Uranus We don t know so much about these distant worlds. The moons closer to Uranus may be more active. Miranda Ariel Titania Oberon
Neptune s moon Triton a young and active surface. Is it a cousin of Pluto heated by tides when it was captured by Neptune?
Asteroids Remnants of the building blocks the planets were made from. Irregular shapes come from a long history of impacts. Gaspra Ida Eros
Asteroids are not all the same! Itokawa was visited by Hayabusa, a Japanese spacecraft. It collected a soil sample and brought it back to Earth. Only 600 m long, is it a loose pile of rubble? Lutetia, 100 km across, was imaged by Rosetta, a European spacecraft on its way to a comet. Are the lines on its surface cracks made by impacts? JAXA ESA
Comets icy cousins of asteroids. Building blocks of most of the outer solar system. When they approach the sun their ices evaporate into space Wild 2 Tempel 1 Hartley 2 Comet Halley
The solar system is a big neighborhood and the neighbors are very different. The biggest surprise of solar system exploration has been this extraordinary diversity.